The present invention generally relates to mixed powder for powder metallurgy to be used in the manufacture of sintered parts, brushes and so on, and particularly relates to iron-based powder for powder metallurgy suitable for the manufacture of iron sintered parts superior in rust prevention performance to be used as solid lubricants and the like, as well as to an iron sintered body.
Generally speaking, iron powder used for the purposes of sintered machine parts, sintered oil retaining bearings, metal graphite brushes and so on rusts easily, and is generally used by mixing an organic rust preventive agent such as benzotriazole therein.
Nevertheless, although such an organic rust preventive agent has a temporary rust prevention effect, since it dissolves or becomes vaporized at a temperature of 500° C. or higher, it will disappear at an ordinarily used sintering temperature of 700° C. or higher. Therefore, after sintering, this will become the same state as when no rust prevention measures are taken, and there is a problem in that the iron powder will rust extremely easily.
Meanwhile, in order to obtain rust prevention properties after sintering, proposals have been made for obtaining a composite powder sintered body by mixing minute amounts of metal powder such as zinc, bismuth or lead with the iron-based sintering powder, or mixing the vapor thereof to the gas upon sintering.
Nevertheless, since this will increase new processes, there is a problem in that the manufacturing process will become complex and, as a result, there will be variations in the quality.
As a conventional powder metallurgical additive, there is an additive having organic acid cobalt metal soap as its component, and technology is disclosed for manufacturing a sintered body by adding and mixing this at 0.1 to 2.0% by weight, and molding and sintering this mixed powder (e.g., refer to Japanese Patent Laid-Open Publication No. H10-46201).
Further, disclosed is technology of adding and mixing metal stearate to, and thereafter dry-pulverizing, a rare earth-iron-boron permanent magnet alloy coarse powder mainly composed in atomic % of rare earth element R (among rare-earth elements containing Y, one or two or more elements are combined) of 10 to 25%, boron B of 1 to 12%, and the remaining part consisting of iron Fe, wherein a part of Fe is replaced at least with one or more kinds of elements selected from Co, Ni, Al, Nb, Ti, W, Mo, V, Ga, Zn and Si in a range of 0 to 15%, if necessary (e.g., refer to Japanese Patent Laid-Open Publication No. H6-290919).
Further, disclosed is a molding improving agent which consists of alloy powder for permanent magnets obtained by compounding at least 1 type of stearate to at least one type selected from polyoxyethylene alkyl ether, polyoxyethylene monofatty acid ester and polyoxyethylene alkylallylether at a compound ratio of 1/20 to 5/1 (e.g., refer to Japanese Patent Laid-Open Publication No. S61-34101).